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re: heating question
23 sep 2003
nina  wrote:

>my house is about 2000 sq ft,not sure how many cubic.

about 8x2000, but the volume isn't very important for heating.

>...the kitchen window faces pikes peak, so thats west.

nrel data say january is the worst-case month for solar heating in colorado
springs, when 1450 btu/ft^2 of sun falls on a south wall and 800 falls on
a horizontal surface on an average 28.8 f day with a 41.4 average daily max.
this is a very good climate for solar heating.

> room has a sliding glass door facing south, it does get heat and light.

you might add on a sunspace. a square foot of r2 glazing with 80% solar
transmission might gain 0.8x1450 = 1160 btu on an average jan day and
lose about 6h(65-28.8)1ft^2/r2 = 109, for a net gain of 1051 btu, like
a 50 watt heater that runs for 6 hours per day. 

>anyway, my philospohy is "you pay for the heater everytime youuse it, but
>only pay for a sweater once".

like "you only pay for a sunspace once." it can also add useful floorspace.

>what i want to do is keep my personal space warm during the day, i find that
>me in my room w/a humidifier keeps me cozy.

a heater would be frugaler. the low-temp oil-filled jobs seem safe.

>but i am not sure about the rest of the house, i hate to heat the whole place
>just to get a few rooms warm. i do not trust anyone here with a space heater.

you might seek psychological help, or add enough insulation and thermal mass
to your room to keep it warm when the furnace is off. with thermal shutters
for cold nights and cloudy days. if your room is, say, 8'x8'x16' deep, with
an 8'x8' window, and you add r7.2 ($10 sheets of atlas 4'x8'x1" double-foil
polyisocyanurate foamboard) to its 640 ft^2 of surface, its heat conductance
would be about 640 ft^2/r10 = 64 btu/h-f. 

>when is the best time to turn the heat up so that when the other people get
>here the house is warm?

depends on the furnace capacity and the amount of thermal mass in the house.
drywall has about 1 btu/f per board-foot. a 50k btu/h furnace might warm 20k
btu/f of house thermal mass from 50 to 70 f in 20kbtu/f/(50k btu/h) = 0.4
hours, ie 24 minutes. a forced-air furnace could warm the air quicker. a
clever person or thermostat might up the air temp until the walls warm, in
order to provide greater comfort. a 90 f room with 50 f walls might feel
the same as a 70 f room with 70 f walls. 

>at night, how low should i allow it to go.

fifty is frugal... 30 is not, with frozen pipes. if the house is 50 for
16 hours per day, your average 65 f room with the doors closed and window
shuttered would lose about 16h(65-50)64 = 15.4k btu/day of heat, which
might come from 15.4k/(70-60) = 1540 btu/f of thermal mass cooling from
70 to 60 f. you might make an attractive and frugal bottle gabion column
and coffee table to store heat. 

place one 2-liter soda bottle filled with water vertically on a strong floor,
surround it with 8 radial bottles, necks inward, wired in a ring, put another
radial layer on top, and so on. build one around a pole lamp for more interior
drama. all this water could come in handy if well pump power fails during a
hurricane... 8 vertical bottles and 26 radial layers of 8 would weigh 4.4x216
= 950 pounds, with a 950 btu/f thermal capacitance.

>im not sure how to determine if its cheaper to keepit cold then heat it,

cooler is always cheaper, even with heat pumps, if it's warmed slowly. 

>or what temperature is the best to maintain so that im neither wasting
>too much heat or using too much to defrost the place.

fifty. you might see small drywall cracks, but these can be filled with
flexible white caulk.

have you thought about coming to the conference in boulder next week?

sustainable resources fall 2003 conference
"resources for the developing world"

caryn rogers and i have planned to do a workshop on "ohm's law for heatflow"
with applications to frugal solar water and house heating and natural cooling
on saturday afternoon 10/4/03 from 1:30 till 3:30.

we've planned to provide arithmetic tools and data and strategies needed for 
effective house heating and cooling using local materials and skills, and to
discuss power, energy, heatflow, and overnight and cloudy day heat storage at
the high-school math level, with insulation and heat capacity of materials,
simple equations involving time constants, evaporative and night ventilation
cooling, climate data, and schemes for 100%-solar house heating and natural
cooling, and give away a cd-rom. techniques include sunspaces and shelfboxes,
"pancake houses," soap bubble insulation, and concentrating solar attics that
might collect both heat and electricity from water-cooled pv panels. 


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